This invention relates to current sensor arrangements, and more particularly to current sensor arrangements which use magnetic sensing devices which may be, or are, subject to unit-to-unit variation as a result of manufacturing tolerances, andor which, once manufactured, may be subject to errors or deviations as a result of temperature variations, aging, and the like.
Seagoing vessels, regardless of whether they are intended for sport, commerce, or warfare, share in common the need to maintain their buoyancy and control in the face of potentially violent conditions including storms, grounding, andor hostile action. Maintaining control and buoyancy in the face of damage due to such violent conditions may require rapid amelioration of, or adaptation to, such damage. In a large ship, there may be many compartments, the entrances to which are separated by a sufficient distance from each other so that considerable time may be required for movement from one compartment to another. The existence of such compartments has in the past given rise to the need for an observer assigned to each compartment or set of compartments to monitor conditions. It might be thought that speaker tubes or telephones would be suitable for communicating between each of the various compartments and a control center or bridge, but there is a real possibility that damage to a compartment might also damage the communications equipment. Consequently, warships assign crew members to be messengers, whose duty is to carry information from the compartments to the control center or bridge in the event of a break in the communications. Damage to one compartment of a ship may require adjustments in many compartments, as for example when flooding of a compartment requires redistribution of the ship""s load or supplies to prevent excessive list. The adjustments may include operation of valves and switches within the compartments, as might be required, for example, to start pumps and open valves for the dumping overboard of bilge water, or for redistributing liquid fuel from tanks on one side of the ship to tanks on the other side. Because time is very important when attempting to cope with damage, warships have in the past stationed crews at various locations about the ship. These crews are charged with the duties of operating valves and switches as commanded or trained. In addition to such adjustments, additional crews must be provided to be on standby for firefighting, for damage repair, and for tending the injured. In the case of a warship, a portion of the crew must additionally be used for manning weapons and countermeasure. Since the tending of injured presupposes that some of the crew is not capable of performing its duties, the crew must, even when reduced in number by casualties, be large enough to be able to perform all of the tasks associated with tending a ship in distress. All of these considerations result in the manning of ships with crews large enough to provide xe2x80x9csurgexe2x80x9d capability for the handling of any emergency. A large battleship of WWII vintage had a crew in excess of 3000 men, and an aircraft carrier in the vicinity of 5000. Even modern missile destroyers require crews exceeding 300 persons.
The presence of such large crews inevitably has its effects on ship design. It will be clear that the housekeeping and support requirements tend to expand disproportionally as the crew grows larger. The ship itself must be large in order to hold the oversize crew, and must carry additional stores such as food, which makes it larger still. Food preparation areas must be larger with a large crew, and the additional food preparation personnel in turn require their own support staff and ship facilities. The cost of ships is adversely affected by the need for a crew of a size to provide surge capability, and the cost of operating such ships is directly increased by the supernumerary members of the crew. The operating cost is further increased by the need to maintain the supernumerary members. It is thus of great importance in ship design to take into account the staffing requirements of the ship, and to improve ship design in such a manner as to minimize the crew size.
The Navy has recognized the disadvantages of such large crews, and is examining ways in which automation might reduce crew sizes. In some proposed systems, automation controls valves, electrical motors, and the like by way of a reliable local area network. xe2x80x9cSmartxe2x80x9d controls coupled to the local area network monitor the status of the various components of the ship, make relatively autonomous decisions as to the actions to be taken in response to various sensed conditions in view of the state of ship readiness which an operator sets, and implements the decisions by operating various valves and equipments. Many of the equipments are electrically operated, such as ship drive, gun slewing mechanisms, weapon hatches, fuel pumps, and other motor-driven devices. It is desirable to monitor the electrical load current of such motor-driven devices to aid in determining the state of the device itself, and also to determine that the commands are being carried out. Load current may be monitored by means of electrical current sensors.
Improved current sensors are desired.
A current sensor arrangement for measuring a subject electrical current flow includes an elongated conductor having fixed dimensions, which is to stay invariant with time. The elongated conductor is configured for producing a generally planar magnetic field within a spatial region adjacent the conductor when the subject electrical current flows through the elongated conductor. A magnetic field sensing or measuring device is located in the spatial region with a particular direction generally parallel to the planar magnetic field. The magnetic field sensing device produces a signal voltage in response to a magnetic field in the particular direction therethrough, and the magnitude of the signal voltage is approximately linearly related to the magnitude of the magnetic field in its vicinity, at least over a limited range of magnetic fields. The magnetic field sensing device may be either temperature-dependent, variable in its sensitivity from device to device, or both, or neither. The magnetic field sensing device produces a magnetic-field-representative signal voltage in response to the magnetic field. The current sensor arrangement also includes a controllable test or bias current generator magnetically coupled to the spatial region, for, when energized, generating a test current flow, which may be a predetermined current flow, for generating a test or bias magnetic field component in the spatial region. The test magnetic field component is desirably generally parallel with the planar magnetic field, whereby, or as a result of which, the magnetic field sensing device produces a magnetic-field-representative signal voltage related to the magnitude of the sum of the subject electric current with the test current. A control arrangement is coupled to the magnetic field sensing device and to the test current generating means, for recurrently energizing the controllable test current generating means, and for determining the magnitude of the current flow in the elongated conductor from at least (a) the magnitude of the magnetic-field-representative signal voltage during those times during which the controllable test current generating means is energized, (b) the magnitude of the magnetic-field-representative signal voltage during times in which the controllable test current generating means is not energized, and (c) the magnitude of the test current.
In a particular manifestation of the invention, the recurrent energization is periodic. Among the magnetic field sensing devices for which the invention is usable are giant magnetoresistive device and spin-dependent tunneling devices. In one distinct version of the invention, the test current generator is galvanically coupled to the elongated conductor adjacent the spatial region, for causing the test current to flow through the elongated conductor and thereby generate the test magnetic field within the spatial region. In this distinct version, the control arrangement comprises a switching arrangement, for, when in the conducting state, gating the predetermined current to the elongated conductor, and for, when in the nonconducting state, preventing the predetermined current from flowing in the elongated conductor. The galvanic connections may be made by current conductors connected to the elongated conductor on either side of the spatial region.
In another distinct version of the current sensor arrangement according to the invention, the controllable test current generator comprises a second electrical conductor extending through the spatial region, electrically isolated from the elongated conductor, and preferably parallel therewith. In this other distinct version, the control arrangement includes a switching arrangement, for, when in the conducting state, gating the test or predetermined current to the second electrical conductor, and for, when in the nonconducting state, preventing the test or predetermined current from flowing in the second electrical conductor.